<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<style>
.descendants *
{ 
	display: block;
	border: 2px solid lightgrey;
	color: lightgrey;
	padding: 5px;
	margin: 15px;
}
</style>
<script src="https://cdn.staticfile.org/jquery/1.10.2/jquery.min.js">
</script>
<script>
$(document).ready(function(){
  $("div").find("span").css({"color":"red","border":"2px solid red"});
});
</script>
</head>
<body>

<div class="descendants" style="width:500px;">div (当前元素) 
  <p>p (儿子元素)
    <span>span (孙子元素)</span>     
  </p>
  <p>p (儿子元素)
    <span>span (孙子元素)</span>
  </p> 
</div>

</body>
</html>